题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4190

Distributing Ballot Boxes

Time Limit: 20000/10000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 1065    Accepted Submission(s):
536

Problem Description

Today, besides SWERC‘11, another important event is
taking place in Spain which rivals it in importance: General Elections. Every
single resident of the country aged 18 or over is asked to vote in order to
choose representatives for the Congress of Deputies and the Senate. You do not
need to worry that all judges will suddenly run away from their supervising
duties, as voting is not compulsory.
The administration has a number of
ballot boxes, those used in past elections. Unfortunately, the person in charge
of the distribution of boxes among cities was dismissed a few months ago due to
nancial restraints. As a consequence, the assignment of boxes to cities and the
lists of people that must vote in each of them is arguably not the best. Your
task is to show how efficiently this task could have been done.
The only
rule in the assignment of ballot boxes to cities is that every city must be
assigned at least one box. Each person must vote in the box to which he/she has
been previously assigned. Your goal is to obtain a distribution which minimizes
the maximum number of people assigned to vote in one box.
In the first case
of the sample input, two boxes go to the fi rst city and the rest to the second,
and exactly 100,000 people are assigned to vote in each of the (huge!) boxes in
the most efficient distribution. In the second case, 1,2,2 and 1 ballot boxes
are assigned to the cities and 1,700 people from the third city will be called
to vote in each of the two boxes of their village, making these boxes the most
crowded of all in the optimal assignment.

Input

The fi rst line of each test case contains the integers
N (1<=N<=500,000), the number of cities, and B(N<=B<=2,000,000), the
number of ballot boxes. Each of the following N lines contains an integer
a_i,(1<=a_i<=5,000,000), indicating the population of
the i^th city.
A single blank line will be included after each
case. The last line of the input will contain -1 -1 and should not be
processed.

Output

For each case, your program should output a single
integer, the maximum number of people assigned to one box in the most efficient
assignment.

Sample Input

2 7

200000

500000

4 6

120

2680

3400

200

-1 -1

Sample Output

100000

1700

题目大意：有n个城市，b个投票箱，接下去的是每个城市的人口数，最后输出每个投票箱的容量是多少。

题目思路：对投票数进行二分，然后对箱子数进行匹配，人口数除以箱子的容量就是城市分配的箱子数。

详见代码。

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cmath>
 4
 5 using namespace std;
 6
 7 int main ()
 8 {
 9     int a[500001];
10     int n,b,ans,Max;
11     while (~scanf("%d%d",&n,&b))
12     {
13         if (n==-1&&b==-1)
14             break;
15         Max=0;
16         for (int i=0;i<n;i++)
17         {
18             scanf("%d",&a[i]);
19             if (Max<a[i])
20                 Max=a[i];
21         }
22         int l=0;
23         int r=Max;
24         int sum,mid;
25         while (r>=l)
26         {
27             sum=0;
28             mid=(r+l)/2;
29             for (int i=0;i<n;i++)
30             {
31                 sum+=ceil(a[i]*1.0/mid);
32             }
33             if (sum>b)
34                 l=mid+1;
35             else
36                 r=mid-1,ans=mid;
37         }
38         printf ("%d\n",ans);
39     }
40     return 0;
41 }